递归显示二叉树

Question

我的代码可以在 16 位汇编器中正确地将节点添加到树中。我可以毫无问题地显示任意数量的左树。每次我试图让正确的孩子打印它时，系统都会崩溃。我试图查看 turbo 调试器中发生了什么，并假设我没有正确保存或弹出堆栈。

我通过 turbo 调试器运行此代码的次数超出了我的记忆，并且无法查看问题出在哪里。

.MODEL small
.STACK 100h

.DATA
menuchoice DB 10, 10, 13, 'Please enter your choice from the menu. $'

message DB 10, 10, 13, 'Please enter the character you would like to add (enter # to exit): $'

menu    DB 10, 10, 13, 'Binary Search Tree Menu'
        DB 10, 10, 13, '1 - Add a character to the tree'
        DB 10, 10, 13, '2 - Search the tree for a character'
        DB 10, 10, 13, '3 - Display the contents of the tree'
        DB 10, 10, 13, '4 - Exit the program $'

empty   DB 10, 10, 13, '     The tree is empty. $'

crlf    DB 10, 13, '     $'

bintree DB 60 DUP(0) ; create a list with a size of 20 characters

node    DB 0 ; node starts at zero become 1 once value is added
root    DB 1 ; next available slot
next    DB 1 ; next is the pointer to the next slot for the character


.CODE
tree PROC
     ; first two lines in main in all assembler 
       mov ax, @data
       mov ds, ax

DISPLAYMENU: ; set up my label

     ; display menu
       mov dx, OFFSET menu
       mov ah, 09h
       int 21h

     ; display menu choice prompt
       mov dx, OFFSET menuchoice
       mov ah, 09h
       int 21h

     ; get the character from the keyboard with echo
       mov ah, 01h
       int 21h

MAINLOOP: ; set up my label

     ; compare data entry to 4 to exit program
       cmp al, 34h
       je exitprog

     ; compare data entry to 1 to add node
       cmp al, 31h
       je starttree

     ; set root to 1
       mov root, 1

     ; determine if tree is empty, if empty display message
       cmp node, 0
       je emptymessage

     ; compare data entry to 2 to search tree
       cmp al, 32h
       jne check3
       call searchtree

CHECK3: ; set up my label

     ; compare date entry to 3 to display data
       cmp al, 33h
       jne mainloop
       call disptree

       jmp mainloop

     ; set si to zero to represent empty
     ;  mov si, 0

     ; set di to zero to represent empty
     ;  mov di, 0

EXITPROG: ; set up my label       

     ; exit to DOS
       mov al, 0
       mov ah, 04ch
       int 21h

EMPTYMESSAGE: ; set up my label

     ; display empty message
       mov dx, OFFSET empty
       mov ah, 09h
       int 21h

     ; move back to main
       jmp displaymenu

STARTTREE:  ; set up my label

     ; display message
       mov dx, OFFSET message
       mov ah, 09h
       int 21h

     ; get character from keyboard with echo
       mov ah, 01h
       int 21h

       mov ah, 0

     ; check to see if the character entered is #
       cmp al, 23h

     ; if equal jump to exit program
       je exitprog

       mov root, 1

     ; compare next to 60 to determine if there is still space in the tree if not exit
       cmp next, 60
       jnl exitprog

CHECKTREE: ; set up my label

     ; check to see if tree is empty and jump to addnode if equal
       cmp node, 0
       je addnode

     ; compare root to zero and jump to addnode if equal
       cmp root, 0
       je addnode

     ; if not equal then jump to evaltree
       jne evaltree

ADDNODE: ; set up my label

     ; change node value to 1
       mov node, 1

     ; move the array position value in next to si
       mov bl, next
       mov bh, 0
       mov si, bx

     ; move the value into tree
       mov [bintree + si], al

     ; increment next by 3 to move position to next character slot
       add next, 3

     ; jump back to menu
       jmp displaymenu

EVALTREE: ; set up my label

     ; move root to di to compare position
       mov bl, root
       mov bh, 0
       mov di, bx

     ; compare bintree to value
       cmp al, [bintree + di]

     ; if less than jump to left child
       jl leftchild

     ; if greater than jump to right child
       jg rightchild

LEFTCHILD: ; set up my label

     ; subtract 1 from di
       sub di, 1

     ; move the position in bintree + di to root
       mov bl, [bintree + di]
       mov root, bl

     ; compare root to zero and if equal jump to change pointer and not equal to checktree
       cmp root, 0

       je changeptr

       jne checktree

RIGHTCHILD: ; set up my label

     ; add 1 from di
       add di, 1

     ; move the position in bintree + di to root
       mov bl, [bintree + di]
       mov root, bl

     ; compare root to zero and if equal jump to change pointer and not equal to checktree
       cmp root, 0

       je changeptr

       jne checktree

CHANGEPTR: ; set up my label

     ; move next to bintree + di
       mov bl, next
       mov [bintree + di], bl

     ; jump to checktree
       jmp checktree

tree ENDP

searchtree PROC

searchtree ENDP

disptree PROC

     ; save the value in root to the stack
       mov bl, root
       mov bh, 0
       push bx

     ; mov value in root to si
       mov si, bx

     ; decrement si to check the left child of character
       sub si, 1

     ; compare the value in bintree to 0
       cmp [bintree + si], 0
       je ldispret

     ; move the value in bintree + si to root
       mov bl, [bintree + si]
       mov root, bl

     ; return to disptree
       call disptree

     ; get root value from the stack
       mov root, bl

     ; move root to si
       mov bl, root
       mov bh, 0

DISPRIGHT: ; set up my label

       mov si, bx

     ; display the character
       mov dl, [bintree + si]
       mov ah, 02h
       int 21h

     ; increment si to check the right child of the character
       add si, 1

     ; compare the value in bintree + si to 0
       cmp [bintree + si], 0
       jne goright
       jmp rdispret

GORIGHT: ; set up my label

     ; move the value in bintree + si to root
       mov bl, [bintree + si]
       mov root, bl

     ; go back to disptree
       call disptree

ldispret: ; set up my label
     pop bx
     pop ax
     push bx
     push ax
     ret

rdispret: ; set up my label
     ; mov cl, root
     ; add cl, 3
     ; cmp next, cl
     ;je tomain 

     pop bx
     pop bx 

     jmp dispright

     pop bx
     pop bx
     ret

disptree ENDP 

TOMAIN: ; set up my label

     ;jmp mainloop

       end tree  

当它显示二叉树的内容时，它应该按字母顺序打印字符。如果我的输入是 m, b, a, c 它应该显示 abcm 然后返回菜单。程序在评估正确的树并尝试显示它时崩溃。

Answer 1

遵循您的程序流程并不容易，但我想我设法找到了导致代码崩溃的许多（重要）原因。

; return to disptree
  call disptree
; get root value from the stack
  mov root, bl

disptree 过程使用 ldispret: 中的堆栈操作在堆栈上留下一个单词，但与您上面的评论相反，您没有'不要从堆栈中取出任何东西！使用pop bxmov root, bl。

请注意，第一次调用 disptree（来自菜单的那个）也必须从堆栈中丢弃这个词。

---

rdispret: ; set up my label
  pop bx
  pop bx 
  jmp dispright

和

DISPRIGHT: ; set up my label
  mov si, bx
  ; display the character
  mov dl, [bintree + si]

rdispret: 代码首先弹出一个root 值，然后弹出一个返回地址。它是您随后错误地将其用作 bintree 数组中的索引的返回地址。使用pop bxpop axjmp dispright。

---

对于任何使用递归的程序，最好分配一个大堆栈。 256 字节有点便宜。

---

CHECK3: ; set up my label
  ; compare date entry to 3 to display data
  cmp al, 33h
  jne mainloop

如果用户未能输入“1”到“4”范围内的数字，您的程序将进入无限循环。

如果发生这种情况，您需要向用户请求另一个字符。将 mainloop 标签向上移动 2 行。